The present invention relates to devices for observing and mapping .gamma.-ray emitting objects, and more particularly to a .gamma.-ray detecting device which utilizes a dislocation-free crystal.
The existence of .gamma.-ray astronomical objects is a relatively recent discovery in scientific history. This is primarily due to the high absorption rate of .gamma.-rays by the atmosphere, whereby detection of such .gamma.-ray emitting sources can only be performed from high altitude observatories such as balloon or satellite-borne telescopes. Gamma ray telescopes have been developed to study these celestial .gamma.-ray emitting sources. One of the more interesting regions in the .gamma.-ray spectrum for celestial bodies is in the region of 511 keV. However, at this energy level, the short wavelength of the .gamma.-rays render grazing-incidence .gamma.-ray telescopes substantially ineffective, the upper energy level for such instruments being typically on the order of 40 keV. Coded aperture telescopes can extend the observation region to much higher energies, on the order of 1000 keV. However, no conventional high resolution .gamma.-ray telescopes exist that are suitable for studying .gamma.-rays in the higher intensity, short wavelength regions.
.gamma.-rays have also been used to examine the internal structure or contents of an object. Such examination is generally effective only when a significant spatial variation in the density of the object exists. This limitation is in part a result of (1) the ability of .gamma.-rays to penetrate materials and (2) limitations on the ability to distinguish between target emitted .gamma.-rays and background radiation.
Therefore, there has been a need in the art for an .gamma.-ray detector capable of detecting and resolving high energy .gamma.-rays up to 10-20 MeV. There has also been a need for an .gamma.-ray imaging system that is capable of examining the structure or contents of an object in a reliable manner.